I'm having the same issue with Ender 3 V2. Everything tightened, Z-axis coupler not "slipping"... I noticed, that the error is made by the Z-axis end switch itself. I am not sure how that is possible but try homing several times and you'll see that the loud click when the switch is triggered occurs in a span of +/- 3 mm, which then results in a ...
Sounds like you have incorrectly set up your machine, specifically the Z offset.
Or your Z endstop is physically too low and not set up properly.
I'd suggest recalibrating your machine from the start as that would help dial it in as well as potentially solve this issue.
I recommend following this guide at the Teaching Tech 3D Printer Site - it's extremely ...
I finally found the problem. The threaded rod of the Z axis was not mounted tight enough to the motor. This resulted in the slipping of the Z axis by large accelerations of the motor.
So... tightening the threaded rod connector socket and redoing the leveling solved the problem.